Characterization of geometrically necessary dislocation evolution during creep of P91 steel using electron backscatter diffraction

In this study, the change of geometrically necessary dislocation (GND) has been investigated during the elevated temperature creep of P91 steel. Firstly, the crept microstructures of P91 steel at 873 K and 165 MPa were characterized by electron backscatter diffraction (EBSD). Then, the resultant GND distributions were analyzed in detail. Meanwhile, the GND density was quantitatively estimated by two methods of kernel average misorien-tation (KAM) and Nye's dislocation density tensor, respectively. The obtained results indicated that during creep of P91 steel, the values of GND density calculated by the KAM method are highly consistent with those of Nye's dislocation density tensor method. Besides, the GND density increases significantly during the initial creep stage and attains the maximum approximately at the transition from initial creep to steady creep. During the subse-quent creep, it gradually decreases. In addition, it suggested that the internal stress predicted by the obtained GND density is consistent with previous experimental data. Accordingly, it further demonstrated that the present characterization of GND evolution offers a convenient tool for the microstructure degradation analysis of P91 steel during creep.

Automated summary

This study investigates the change of geometrically necessary dislocation (GND) during the elevated temperature creep of P91 steel. The results show that the GND density increases significantly during the initial creep stage, reaches a maximum at the transition from initial creep to steady creep, and gradually decreases during subsequent creep. It also demonstrates that the GND density can be used to predict internal stress and analyze microstructure degradation of P91 steel during creep.